Preheat the broiler. Cover a baking sheet with foil. Place the tomato, white onion, garlic and Anaheim chiles on the baking sheet and roast under the broiler for about 10 minutes, turning the vegetables halfway through, until charred and the tomatoes have begun to release their juices. The garlic will probably be done before the other vegetables. Remove them from the heat when charred. Alternatively, you can char everything on a preheated comal, skillet or griddle set over medium-low heat, or on a grill. Remove from the heat.
Transfer the Anaheim chiles to a bowl and cover tightly or to a plastic bag, and seal. Allow to sweat for 10 minutes, then peel, stem and seed. Peel the garlic when it’s cool enough to handle.
Place the roasted vegetables, including any juices from the baking sheet or bowl, in a blender. Add the lime juice, mayonnaise, crema, mustard, Worcestershire sauce, soy sauce, butter, salt and pepper. Puree until completely smooth.
Position the rack in the middle of the oven and preheat to 450°F. Cover a large baking sheet with aluminum foil. Brush the foil with vegetable oil.
Rinse the fish fillets, pat dry, and place skin side down on the baking sheet. Reserve 1/2 cup of the sauce and spread the rest very generously over the fish, creating a very thick layer.
Bake the fish anywhere from 20 to 30 minutes –- depending on the thickness of the fish, until the fish is cooked through and flakes easily when poked with a fork, and the sauce is nicely browned and a little crusty on top.
Meanwhile, preheat a comal over medium heat, and in a medium bowl combine the bell peppers, slivered red onion and reserved sauce. Toss well.
Heat the corn tortillas on the hot comal for about a minute per side, or until they are heated through and beginning to speckle and very lightly toast on both sides. Place in a tortilla warmer or wrap in a clean kitchen towel.
Place the bell pepper/sauce mix and the tortillas on the table along with the quartered limes and your favorite hot sauce.
Bring the fish to the table as soon as it is ready. Let everyone assemble their tacos with a piece of fish, the peppers and sauce, a squeeze of lime and hot sauce to taste.